1. Field of the Invention
The present invention relates to a multilayer chip capacitor, and more particularly, to a multilayer chip capacitor capable of having a controllable and high equivalent series resistance (ESR) and a low equivalent series inductance (ESL) and embodying uniform impedance characteristics in a wide frequency band and a circuit board device including the multilayer chip capacitor.
2. Description of the Related Art
Multilayer chip capacitors are generally used as decoupling capacitors for stabilizing a power supply circuit, such as power distribution networks of micro processing units (MPUs). Decoupling capacitors are used as low impedance current sources to suppress voltage noise due to simultaneous switching of MPUS.
As the MPU is increased in integration density, its current consumption is continuously increased and operating voltage is decreased. Accordingly, it becomes more difficult to suppress noise of a supply direct-current (DC) voltage according to a sudden change of a consumed current of an MPU. Recently, the consumed current is changed more rapidly with the increase in an operating frequency of the MPU. Accordingly, it is required to increase a capacitance and an ESR of a decoupling capacitor and reduce an ESL thereof. This is for maintaining magnitude of an impedance of a power distribution network to be low and uniform within the broadband frequency range. Ultimately, this is helpful to suppress noise of a supply DC voltage from a sudden change of a consumed current of an MPU.
To satisfy ESL characteristics required in decoupling capacitors used in an MPU power distribution network, changes to the arrangement of an outer electrode and a shape of an inner electrode of a capacitor have been provided. For example, U.S. Pat. No. 5,880,925 discloses a method of reducing an ESL by disposing leads of a first inner electrode and a second inner electrode in an interdigitated arrangement to form many and short current paths in the capacitor. This method is capable of reducing an ESL but entails a reduction of an ESR besides the ESL. Stability of a power supply circuit depends on not only an ESL but also an ESR. An excessively small ESR deteriorates the stability of a power supply circuit, thereby suddenly changing a voltage due to power network resonance. Such capacitor effectively reduces high frequency impedance. However, due to the excessively small ESR, it is difficult to maintain the magnitude of an impedance of a power distribution network to be low and uniform.
To overcome a problem of the excessively low ESR, there has been provided a method of embodying high ESR characteristics by using electrical high-resistance materials for an outer electrode or an inner electrode. However, when using high-resistance outer electrodes, it is difficult to prevent localized heat spots caused by a current concentration phenomenon due to pinholes in outer electrodes and to accurately control ESR. Also, when using high-resistance materials for inner electrodes, disadvantageously, high-resistant internal electrode materials should be changed with the improvement or change of ceramic materials since the high-resistant internal electrode materials should be matched with the ceramic materials, which leads to the increased cost of the products.
U.S. Patent Publication No. 2006/0209492 discloses a capacitor having a low impedance in a wide frequency band by disposing two capacitors having a different capacitance from each other in the same capacitor body. However, as disclosed, it is impossible to maintain an impedance to be uniform around each resonating frequency, thereby having a harmful effect on stability of a power supply circuit.